AQA GCSE Chemistry - History of the Atom

AQA GCSE Chemistry - History of the Atom 1. What is the term used to describe the number of protons present in an atom? Answer: The atomic number. 2. What is the number of electrons in an atom related to? Answer: The number of protons. 3. How do you calculate the number of neutrons in an atom? Answer: By subtracting the atomic number from the atomic mass number. 4. Who described atoms as solid spheres in the 19th century? Answer: John Dalton. 5. What discovery by JJ Thomson led him to modify his atomic model, introducing the concept of electrons? Answer: His measurements of charge and mass revealed the presence of smaller, negatively charged particles (electrons) within atoms. 6. Why is the "Plum Pudding" model named so? Answer: Because it depicted a ball of positive charge with electrons embedded within it. 7. What was the outcome of Rutherford's scattering experiments in 1909 that discredited the Plum Pudding model? Answer: The results showed that some alpha particles were deflected, disproving the model's predictions. 8. How did Rutherford's experiment prove the existence of a nucleus? Answer: The fact that some alpha particles bounced back, indicating a central, positive body (nucleus), was a key finding. 9. How did Bohr's work build upon Rutherford's model? Answer: Bohr proposed that electrons occupy fixed energy levels or shells, preventing them from collapsing onto the nucleus due to attractive forces. 10. What did Rutherford discover about the nucleus? Answer: He found that it could be broken down into smaller particles, leading to the discovery of protons. 11. Who discovered neutrons? Answer: James Chadwick. 12. What is the formula for calculating relative atomic mass? Answer: The formula involves dividing the mass of an isotope by its abundance, then dividing by 100.